000 WTPZ44 KNHC 232042 TCDEP4 HURRICANE HILARY DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092011 200 PM PDT FRI SEP 23 2011 HILARY HAS REMAINED RELATIVELY STEADY STATE IN INTENSITY AND STRUCTURE TODAY AS A SMALL CATEGORY FOUR HURRICANE. THE TAFB AND SAB SUBJECTIVE DVORAK ANALYSES AS WELL AS THE ADVANCED DVORAK TECHNIQUE FROM CIMMS CONTINUE TO SUGGEST MAXIMUM WINDS OF 125 KT ...WHICH IS THE INTENSITY ANALYZED THIS AFTERNOON. THE SIZE OF THE CYCLONE ALSO REMAINS QUITE SMALL AS INDICATED BY THE LIMITED COLD CLOUD ENVELOPE AND A 1621Z CIRA AMSU WIND RADII ESTIMATE. THE HURRICANE IS MOVING TOWARD THE WEST AT ABOUT 7 KT...SLIGHTLY SLOWER THAN OBSERVED EARLIER TODAY. HILARY IS PRIMARILY BEING STEERED BY THE INFLUENCE OF A ZONALLY-ORIENTED DEEP-LAYERED RIDGE TO ITS NORTH. THE CYCLONE SHOULD CONTINUE TOWARD THE WEST OR WEST-NORTHWEST AT ABOUT THE SAME SPEED FOR THE NEXT THREE DAYS OR SO. AT THE EXTENDED RANGE...HOWEVER...THERE CONTINUES TO EXISTS A LARGE SPREAD IN THE TRACK GUIDANCE. THE GFDL..HWRF...AND EXPERIMENTAL GFD5 REGIONAL HURRICANE MODELS RECURVE HILARY TOWARD MEXICO BY IN ABOUT FOUR DAYS DUE TO A VIGOROUS SHORTWAVE TROUGH IMPINGING UPON THE AFOREMENTIONED RIDGE. HOWEVER...ALL OF THE REMAINING RELIABLE GUIDANCE KEEPS HILARY ON A WEST-NORTHWESTWARD TRAJECTORY THROUGH FIVE DAYS...AS THEY DO NOT SHOW ANY SIGNIFICANT INFLUENCE OF THE TROUGH ON HILARY. IT NOW APPEARS FORTUITOUS THAT THE PREVIOUS FORECAST DID NOT INDICATE A TRACK CLOSER TO MEXICO...AS THE 12Z GLOBAL AND GFDN MODEL SUITE HAVE SWUNG BACK TOWARD THE WEST. THE OFFICIAL FORECAST IS ABOUT HALFWAY BETWEEN THESE MODEL RUNS TO THE WEST AND THE PREVIOUS FORECAST TO THE EAST. WHILE HILARY HAS APPARENTLY NOT INTENSIFIED FURTHER TODAY...THE CYCLONE DOES HAVE THE OPPORTUNITY FOR SOME INTENSIFICATION AS IT SHOULD REMAIN OVER VERY WARM WATERS...IN MOIST AIR...AND WITHIN LOW VERTICAL WIND SHEAR FOR THE NEXT THREE DAYS. IT IS QUITE LIKELY THAT HILARY WILL CONTINUE AS A MAJOR HURRICANE DURING THAT TIME. INTENSITY VARIATIONS THAT OCCUR MAY BE DOMINATED BY INTERNAL DYNAMICS...SUCH AS EYEWALL REPLACEMENT CYCLES...WHICH WE HAVE VERY LIMITED ABILITY TO ANTICIPATE. BY DAYS 4 AND 5...THE CYCLONE SHOULD ENCOUNTER GRADUALLY DECREASING SSTS...LESS UNSTABLE AIR...AND INCREASING VERTICAL SHEAR WHICH SHOULD LIKELY RESULT IN A WEAKENING TREND. THE INTENSITY FORECAST IS BASED UPON THE LGEM AND SHIPS STATISTICAL MODELS AND IS QUITE CLOSE TO THE PREVIOUS ADVISORY. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 16.3N 103.1W 125 KT 145 MPH 12H 24/0600Z 16.5N 104.4W 130 KT 150 MPH 24H 24/1800Z 16.8N 106.3W 125 KT 145 MPH 36H 25/0600Z 17.1N 108.0W 120 KT 140 MPH 48H 25/1800Z 17.3N 109.6W 115 KT 135 MPH 72H 26/1800Z 18.0N 113.0W 105 KT 120 MPH 96H 27/1800Z 19.0N 115.0W 90 KT 105 MPH 120H 28/1800Z 21.0N 116.0W 75 KT 85 MPH $$ FORECASTER LANDSEA/STEWART